Brewing alcoholic beverages such as beer, cider, mead or wine through yeast fermentation involves the chemical conversion of carbohydrates into alcohols and carbon dioxide (CO2). In order to make different alcoholic beverages by way of yeast fermentation, different carbohydrates must be used. To produce beer, hops and grains are used. In the case of cider, apple juice is used as a carbohydrate. To make mead, honey is used, whereas, in making wine, juice (typically grape juice) is used. Irrespective of the carbohydrate used, each of the alcoholic beverages produced involves a yeast fermentation process whereby the carbohydrates provided are converted to alcohol and CO2.
One of the most commonly produced yeast fermented alcoholic beverages is beer. Discussed hereinafter are some of the shortcomings associated with known methods of brewing beer. However, those skilled in the art will recognise that these shortcomings have relevance in equivalent techniques in producing cider, mead or wine.
Brewing beer through fermentation involves a process in which water and extract from grain and hops are fermented with yeast in a fermentation vessel. During the fermentation process the yeast acts on the extract from the grains and produces ethanol, carbon dioxide and flavouring chemicals. The ethanol and flavouring chemicals remain in the beer but the CO2 is emitted out of the vessel. Thus after fermentation the beer is flat and non-carbonated and requires post-fermentation carbonation. After fermentation the yeast usually flocculates down to the bottom of the fermenting vessel and needs to be separated from the beer to avoid yeasty off-flavours being absorbed into the beer. On the small scale, many home brewers siphon the beer off the sediment into another vessel for maturation. The reason for this is that home brewers generally use small flat bottomed fermenting vessels. The maturation stage is ideally a cold period which may involve a clarification step using special clarifying agents such as gelatine and isinglass finings.
In all scales of brewing from large to homebrew scale, the beer is typically flat after fermentation and maturation. In order to carbonate the beer, large breweries recover the CO2 emitted during fermentation into tanks and dose it back into the beer at filtration. Small breweries buy CO2 in tanks and similarly dose it into the beer during filtration. Home brewers will either transfer the matured and clarified flat (non-carbonated) beer into kegs for forced carbonation from an external source prior to consumption (which takes about 5 days) or transfer it into bottles and add some sugar before sealing, for a natural secondary in-bottle fermentation and thus biological carbonation (by yeast) prior to consumption (which takes about 2 to 4 weeks). Where secondary fermentation in bottles is employed for the purposes of carbonation, it can be difficult as well as time-consuming to carbonate the beverage to the correct level. Under-carbonation may occur whereby the beverage is flat, or over-carbonation may occur, which can result in excessive foaming during pouring, or exploding bottles during storage. Such problems are well known and commonly experienced by home brewers.
For carbonation of draft (kegged) beer, which is equally as popular as bottled homebrew, home brewers need to pressurise the keg for about 5 days with CO2 or a mixed gas (usually containing nitrogen and CO2) from an external source, at a specific pressure depending on the temperature of the beer. The CO2 gradually enters the beer until equilibrium is achieved and in this way the correct carbonation is obtained accurately, with more ease and in less time than in the case of bottled homebrew. The disadvantages of carbonating the beverage using an external source of CO2 or mixed gas are that this method requires transferring of the beer which leads to a higher risk of oxygen uptake and microbial contamination. In addition, the source of CO2 or mixed gas is not natural and may contain trace amounts of oxygen or other contaminants. Furthermore the carbonation step can involve a long time period (for example 5 days or more), and is generally inconvenient due to the effort and extra equipment required.
It can be seen that the traditional brewing route contains several steps where the beer is transferred from one receptacle to another. These transfers are time-consuming and increase the chance of infection from bacteria and wild yeasts. It also requires cleaning of lines and vessels before and after each step. Most importantly, these transfers have the disadvantage of introducing oxygen into the beer. The introduction of oxygen after the fermentation stage is very undesirable. Such contact promotes the formation of staling chemicals such as trans-2-nonenal, benzaldehyde and 2-furfural. Even a small amount of oxygen such as 100-400 parts per billion, as is present in a typical bottle of commercial beer after filling, can have a deleterious effect on beer and this is the main reason that commercial beer brands have a use-by date on their product.
Home or small scale brewers use siphon hoses and plastic buckets and usually cannot flush air out of such lines and receptacles with special de-aerated water or CO2 flushes before transfers, as is the case in commercial brewing. Therefore oxygen pick-up is often extremely high (in the parts per million or milligrams per liter range) and very damaging.
The sensitivity of beer to processing damage after fermentation is so high, that the world's number one beer brand has a shelf-life stated on each pack of only 110 days, purely due to the fear that consumers will notice the oxidized flavours that form as beer ages and then switch loyalty to other fresher tasting brands. Even 50 parts per billion oxygen (50 micrograms per liter) in beer causes oxidation of the product over time.
For home brewing, unwanted infection by bacteria and wild yeast can also diminish the quality of the beer. Transfers from vessel to vessel require that all equipment such as all siphon hoses, tools, tanks, kegs and bottles used by the home brewer be properly cleaned and sanitised in order to avoid such infection. This need increases both the time and labour required by the hobbyist and the amount of cleaning chemicals required, which is more detrimental to the environment. Many home brewers have experience producing quality beer in a fermenter, only to ruin it by having an infection in a subsequent maturation vessel, draft beer vessel or bottle.
In addition, home brewers often experience problems of temperature control during fermentation, maturation and dispense. Many home brewers do not use any temperature control and this has a negative impact on the yeast performance, beer flavour and final beer clarity. Control to +/−0.2° C. at all stages of brewing is preferable when making beer at any scale.
So in summary, it can be seen that there are several factors that tend to reduce the quality of beer produced by home or small scale brewers. Firstly, almost all home brewers use vessels that are not pressure vessels, so the CO2 produced during fermentation must be allowed to escape though an air-lock. The fact that carbonation is lost to atmosphere during fermentation means the beer is flat and requires a carbonation step of some kind after fermentation. This leads to more transferring of the beer which leads to a higher risk of oxygen uptake and microbial contamination. The carbonation step involves a long time period for both draft and bottled homebrew and carbonation control in bottles is extremely difficult. Secondly, temperature control during fermentation, maturation, clarification and dispense is also difficult and ideally requires both heating and refrigeration if beer of a professional quality is desired to be produced. Thirdly, in order to remove the sediment resulting from the brewing process, the beverage after fermentation is usually required to be transferred off the yeast, which leads to more handling, a greater risk of infection and an increase in oxygen pick-up which in turn leads to increased staling of the beer.